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2 Repeaters 1 Hardline/antenna

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otobmark

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I have 2 UHF repeaters with duplexers, 1 amateur and the other public safety (460.xx out). At first I was looking at extra cans and circulators to do it properly but the cost kept going up for COTS solutions. At this point I'm thinking I can get by with a NON-SIMULTANEOUS solution, where only 1 repeater at a time can transmit. So, while 1 repeater is active the other is suppressed. If memory serves there are pins on the back of the xpr repeaters that will suppress/knock down the repeaters as well as corresponding busy signal pins. The repeaters would be Tee'd into the hardline or for less loss maybe switched if I can find a reasonably priced switch that is fast enough (Pin diode??). Additionally, can I adjust the dwell at repeater (knock down timer?) to keep conversations from being interrupted by other repeater? I'm guessing the receivers of the repeaters are active even while suppressed/knocked down and thus vulnerable if using pass filters (on amateur). At this point traffic on both repeaters is low and if this works would buy me some time before needing splitter/combiner. Am I on the right track or just suffering from toilet paper deprivation?
 

mmckenna

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Maybe I'm misunderstanding something, but combining amateur and public safety systems like that is a colossally bad idea.

You'd need to work out some way of making sure the public safety side would, without fail, boot the hams off their repeater.
Proper isolation of the systems would be important, even if only one was working at a time.

Maybe I'm not understanding it, but why? Whats the rush on the amateur radio side that can't wait?
 

Flyham

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I think what Oto is getting at is more of a concern of real estate on an up the tower.

Having repeaters for both services, in the same rack isn't (or shouldn't) necessarily be an issue, especially when they are the same make/model.
So yes, any solution that allows both repeaters to use the same feedline and antenna while avoiding the need for any additional transmit/RX combiners would certainly catch my attention as well.
 

mmckenna

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Yeah, that I get.
Doing it with the circulators and combiners would be the right way. But, yeah, it can be expensive. A lot of ways thing can go wrong if you try to hack together a home brew solution. I'd really want a system that would preempt the amateur repeater if the public safety side was in use.

My concern is that an improperly designed system could result in some serious de-sense if the amateur side was transmitting and the public safety side was trying to RX. The risk of missing a weak transmission from a public safety user would keep me up at night.
 
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If the Pass/Notch duplexers have enough isolation and your coax jumpers are the right length you can make the 2 repeaters work. Had a commercial UHF 2 channel trunk system online for almost 20 years this way.
 

davidgcet

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exactly, to even consider doing this on a public safety system it needs to be done correctly. too bad there aren't many hams left that can build and tune a combiner system, it can be done for low cost and equal quality to a purchased one if they know the theory and how to put it into practice. We used to have a guy that worked for us that would build all our combiners out of converted cans and multicouplers that can be bought cheaply and retuned to the desired frequencies. he taught me a lot of it, but I never was good at doing it from scratch. heck he even made a few from the ground up by building his own cans and couplings just to say he had done it.

my next question though is going to be how well will the uhf antenna match to the ham band? a mismatched antenna is going to be crap and will cause other issues.
 

otobmark

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EDIT---many useful comments came in while I was typing this post so forgive the somewhat terse parts of this post below. Going 2 month's without a haircut can apparently mess with my attitude......
All help is appreciated and will be put to use.




My question was technical not political so I didn't think I'd waste everybody's time with a back story. I was hoping for a technical answer on exactly if and how I could accomplish my goals with minimal degradation. I figured there might be people on the forum who had done something similar with the same equipment. Many years ago I remember a system that was NOT sharing an antenna but was configured so that both transmitters would not come up at the same time. I want that with the added challenge of same antenna. Simultaneous operation would be nice but expensive, power hungry, lossy and did I say expensive?

So, now I guess I need to take the "I'm I a dumb-ass" quiz portion of the posting requirements:

--Both repeaters are UHF DMR xpr8400's but they could be upgraded to newer models.
--one is 441.8625/446.8625 with 4 cavity duplexer, preamp, and moto preselector. The other could be on any of 7 frequencies in the range of 460.xxxx/465.xxxx and the outbound gear not yet purchased (preselector if needed, preamp, duplexer).
--Site is 400' with 7/8" hardline and 8 bay antenna.
--At this point public safety is the SECONDARY user in that it is a test platform for Fire/Rescue Task Force (part of our statewide taskforce which deploys all over the US and Puerto Rico). They are exploring DMR and various equipment manufacturers for some of their unique requirements. Their PRIMARY radio systems are the countywide and the Statewide Trunked systems. So no, they do not need preemption but it would be nice to have and possibly the ham side might preempt the PS side under some circumstances.
--The amateur side is primarily used by AUXCOMM groups, which are a creation of DHS and are NIMS/ICS trained and certified group. Their role continues to evolve but in basic terms is a bridge between amateur and public safety and can if asked fill any of the ps communications slots (dispatcher, COML, COMT, IT, HF ALE & Winlink, air & maritime ops etc). Through agreements and MOU's most of the AUXCOMM people can and do operate on PS frequencies and equipment, including SHARES and other Federal. So, in this particular case the majority of amateurs using the amateur repeater can and will also use the public safety repeater and since most of the TF (paid professional fire/rescue) people in my county are also licensed amateurs they can and will use the amateur repeater as well. In the future there may be a patch from the DMR PS repeater to the statewide trunked system allowing AUXCOMM people to get into system without buying or being issued APX8000's.

So, do I now qualify for advice on my technical issues? If so my snarkyness would transform into pure gratitude!
 
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mmckenna

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--At this point public safety is the SECONDARY user in that it is a test platform...

So, do I now qualify for advice on my technical issues? If so my snarkyness would transform into pure gratitude!
That's useful info. Forgive us, but we DO get a lot of hams that come on here with wild ideas about joining public safety and amateur radio systems together.

No, I haven't built my own setup like that. We use the off the shelf stuff for it. Would be interested to see how it works out for you.

Spacing is far enough apart that it do-able.
 

buddrousa

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RX TX sells what you want it is not cheap but it is doable it just has to be do correctly it also helps and is cheaper if you us a RX antenna and a TX Antenna about 60 feet apart.
 

otobmark

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Thanks guys.
Let's break it down a little:
On the mototrbo repeaters using rear connector, can one repeater knock down the other when it goes active?

As in busy indicator pin on each repeater going to the knockdown pin on the other? Am I understanding that right? Crude pre-emption would be to make knockdown 1 way maybe. Most of the time however the PS guys don't really want to knock auxcomm down and would happily wait their turn.
After I thought about it I would have to use a tee to connect both repeaters because both receivers need to see the antenna at the same time so antenna switch is a non starter I guess. Only 1 antenna available so any 2 antenna solutions don't apply.
 

mmckenna

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Well, if you could set your cans up right, there'd be no need for that, you could run both repeaters at the same time, no issues.
 

prcguy

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The closest I've come to what the OP needs is a custom master receive preselector that had a band pass receive window for the 467 through 469Mhz range and another for the 442-443MHz range so a single master receive antenna could feed unlimited business and amateur repeaters within those ranges. I also had wide spaced transmit combiners with cavity filters and isolators and narrow spaced with 3dB hybrids in the system.

As someone mentioned, and with a knowledgeable person at the reigns, it could be possible to simply combine the antenna outputs of each duplexer to a common T adapter and off to one antenna IF the duplexers provide enough isolation to all transmitters and receivers. An isolater at each transmitter would be mandatory and the preamp(s) would obviously have to be a the receiver output of each duplexer and would probably require some extra filtering to make sure they are not hit with out of band levels that would even begin to create IMD.

All this would require some bench testing and sweeping and a bunch of premade jumper cables close to the calculated lengths needed to combine the two duplexers. It would be a fun science experiment, sort of.
 

otobmark

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Starting to sound like a great opportunity to fail. A while back I saw a video of the guys at Bridgecom building something like this, seems like they had 12 cans total! 4 cans per repeater plus 4 cavity gadget at the feedline. No idea the cost of parts or the losses involved. I was hoping to do this relatively cheap. Radio shop has duplexers lying around everywhere although many are "mobile" duplexers which I hate. The amateur repeater in place has high grade cans (Sinclair Q3220E 406-512mhz) & X265UM narrow preselector 435-470. So what other filters am I looking to need? prcguy seems to be using window filters which I understand are expensive.

Anyway the takeaway seems to be "yes it can be done" but for specifics I'm on my own---no cutting to the front of the line......
 

buddrousa

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One question you have to ask do you want to put lives on the line with home made junk.
You said Public Safety does it matter if it is front line or back up do you want to risk lives?
 

otobmark

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I am excellent at cost benefit analysis (as long as it is not connected to something I personally really really want). If my installed gear begins to fail then I've entered a new phase of life-
 

12dbsinad

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What you're asking to do is not standard practice with LMR, especially public safety. I am not sure about anyone else, but I do not and never will mix public safety and ham radio. Having some weird setup like that means the PS system is no longer mission critical, regardless if it's a test system or not.
 

otobmark

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From memory the antenna was 1.2 swr on 441.8625 (and been in continuous use on that frequency with no failure for almost 7 years) and 1.1 on 460.350 (previous repeater). Network analyzer and TDR when installed (hardline is well past 30 yrs old). Will rescope before altering setup to see if anything has changed of course. The antenna was not flat over entire range but 441 was in a sweet spot and performance in the field has been exceptional and balanced. The site in general performs much better than it should which is why I want to use it instead of our alternate sites. Tower has cellphone array about halfway up and at top we have 1 vhf, 2 UHF, & 1 800mhz antennas. Secure location with UPS and backup generator. It is a good site-I just need 2 uhf repeaters on the same hardline/antenna! Since this is technically a DMR test bed more than part of the com plan for the county we might end up ripping everything out in near future so not very wise to put a lot of money into it. Seems to be a lot more interest in my motives than in the technical aspects of the project on the thread....this is a local government project and they will vet the legal issues. I'm just interested in the engineering and cost.
 

otobmark

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What you're asking to do is not standard practice with LMR, especially public safety. I am not sure about anyone else, but I do not and never will mix public safety and ham radio. Having some weird setup like that means the PS system is no longer mission critical, regardless if it's a test system or not.
For the record, nationwide for 80yrs or more amateurs have installed repeaters on PS towers and buildings sharing sites and site resources. Amateur radio is officially a part of our county and state Emergency Management resource plan. Amateur radios are installed at the State EOC and most county EOC's. In NC and SC amateur sites are not only on State towers but connected by Dept of Public safety microwave networks. Auxcomm is a DHS creation for bringing amateur radio into the EOC and operate BOTH as hams and PS. Many of us are COML's and COMT's. So what is the problem here??? How can the setup be weird since at this point the technology has not been decided or I would not have posted my original question? My intended project will either work or it will not, but if it works it will continue to work reliably. What is your definition of mission critical? In the last 7 years the county trunk has gone down countless times from minutes to hours while the amateur DMR at this site has NEVER gone down even when the public safety repeaters at this site did because generator failed to start (Amateur DMR had robust UPS and lasted till mains restored), so which is more mission critical? Everyone including auxcomm amateurs when activated have immediate access to 2 trunk systems, 4 8TACs, backup conventional repeaters for fire, police, ems and sheriff as well as a simplex plan which is tested weekly by the fire dept anyway. We don't degrade comms we improve them and are a valued part of the responder community.

It is ridiculous that this still needs to be explained. Again I'm asking for help with how to do something from a technical point of view only. Why does it have to be political---this is why in my original post I DID NOT give the back story because I didn't want to waste my and other's time on politics, philosophy or sexual orientation. -----OK, I feel better now... I'm going to inventory my toilet paper, Scotch er I mean hand santitizer and go to bed. And again any help would be great. I think the consensus is that what I want CAN be done, now it's down to how expensive or elegant a solution to use.
 
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